I Swear on the River Styx
by Boooklover12
Summary: "I, Perseus Jackson, swear on the River Styx to protect Harry Potter with my life." Percy never breaks his promises- even the ones he shouldn't have made. One shot unless inspiration strikes.


**Just FYI, I don't own this. This is called fanfiction, people!**

It seemed to happen in slow motion.

Percy just watched as a brilliant green light shot out of Voldemort's wand and arced through the fray, barreling towards Harry. It was aimed straight at his heart.

An eternity seemed to happen in those few milliseconds as Percy relived his memories.

Hecate's face as she watched him make the oath on the river Styx.

 _I, Perseus Jackson, swear on the river Styx that I will protect Harry Potter with my life._

The resounding boom of thunder. Hecate's relieved smile, her lips quirking up at the corners.

 _Percy, stay safe! Please, promise me you'll make it back!_

Annabeth's wide gray eyes as her fingers wrapped tightly around her dagger.

 _I'm sorry Annabeth. But I can't promise that._

Percy remembered grinning and picking her up, swinging her around, and looking into her eyes, rubbing the back of her hand with his thumb.

 _I love you._

 _I know. You're my hero. I'm just worried. You would die for this quest. I can see it in your eyes. You would die for someone you just met._

 _I… I know._

Percy watched as the glowing beam moved ever closer. He thought one last time of Annabeth's face, her withering look he would receive for being a Seaweed Brain.

She loved him. He loved her.

 _I, Perseus Jackson, swear on the river Styx that I will protect Harry Potter with my life._

Percy tensed.

With a single bound, he flung himself in front of Harry, spreading his arms wide.

Harry's eyes widened as Percy jumped in front of him.

Percy had just enough time to send Harry a lopsided grin over his shoulder before the beam hit.

For a tiny piece of time, nothing seemed to move. Harry just stared at Percy with his mouth open, uncomprehending.

Then Percy's eyes glowed green, as if the curse was lighting him up from within. Percy collapsed with a note of finality, his eyes snapping closed before he even hit the ground.

For a few seconds Harry stared incomprehensibly at Percy's lifeless form, incapable of internalizing that the exchange student, the one Ron had thought was a Death Eater, the one that they had finally become friends with after hating and scorning, had just given his life for Harry.

No.

Harry lifted his eyes, locking them with the triumphant scarlet ones across the room.

For a moment, none but they two existed.

Then, as if planned, they began to circle each other.

"You killed my friend," Harry snarled, glaring holes in the Dark Lord.

"Oh, that pretty little thing? He was but a toy, a mere entertainer!" Voldemort laughed, a high cold sound that reverberated across the now silent hall.

Harry let go of his anger and directed it into his words. "You didn't think he was a pretty toy when you tried to kill him in the ministry, now did you, Tom?"

Voldemort's scarlet eyes narrowed into slits. "You think that you can taunt me? Dumbledore is dead! No longer do you have any protection! That old fool merely bought you time, and now, I, the greatest sorcerer the world has ever seen, shall kill you. I have hunted you, as you sniveled behind the skirts of greater men and women and allowed me to kill them for you. Now I shall have my victory!"

Voldemort's eyes narrowed even further as he caressed his wand pointing it delicately at Harry's face. Then, at the sound of a window shattering-

" _Avada Kedavra!"_

" _Expelliarmus!"_

Their spells collided dead center, and released a golden shockwave. Voldemort was pushed back, and Harry flew away, rolling to his feet by the walls of the charms corridor.

Voldemort roared in frustration, raising his wand once more, and pointing it at Harry.

" _Avada-"_

Harry fumbled for his wand, finally gripping it with cold fingers.

" _Reducto!"_

Harry's spell hit the ceiling, buying him the time he needed to get to his feet.

Rocks tumbled from the gaping hole Harry had created, raining down on him and Voldemort.

A rather large boulder hit the ground near Percy, narrowly missing the wizard.

Voldemort's eyes glowed like a cat's in the near darkness, narrowing as they landed on Harry.

The words of the prophecy echoed in Harry's ears- _for neither can live while the other survives._

Harry raised his wand and pointed it at Riddle, but before he could shout his spell, there was a large CRACK, and twenty ministry officials arrived on the scene. Too late, Harry realized the anti-apparition wards must have fallen.

Riddle, obviously realizing he could not fight whilst under the nose of the ministry, gave Harry a cold smile. "You are a fool, Harry Potter. And you will lose. Everything."

Voldemort disapparated with a silent whoosh, but not before the Aurors saw him.

One of them made a choking noise in the back of his throat. "He-who-must-not-be-named, _here_ , in the castle!"

Another auror looked just as shocked. "I saw him too, Williams, I saw him too!"

Harry pulled himself to his feet and reality came crashing down on him.

 _Percy._

 _No._

Vaguely, Harry acknowledged that Hermione and Ron had entered the corridor. He stumbled forward, slowly at first, but quickly breaking into a run.

"Percy!" Harry's voice broke.

"Percy…"

Ron and Hermione were stumbling to Percy's side, quickly dropping to their knees beside his motionless form.

Ron looked up at Harry. "What… What _happened_?"

Harry stared, his mind foggy with incomprehension. "He… He jumped in front of me… Into Voldemort's curse…"

As Hermione reached out to touch Percy's tan fingers, there was a ringing sound up and down the corridor. It echoed between the walls, creating an eerie ringing that sounded impossibly loud in Harry's mind.

" _I, Perseus Jackson, swear on the river Styx to protect Harry Potter with my life."_

The oath trembled up and down the corridor, sending shivers down the spines of all who heard it. There was something other-worldly about the tone of Percy's voice as he said the words, something entrenched in fate.

" _I, Perseus Jackson, swear on the river Styx to protect Harry Potter with my life."_

The oath was repeated once more, and at its completion both Harry Potter and Percy Jackson glowed a brilliant gold. Once the light died down, a new female voice joined the mix.

" _I, the Lady Styx, pronounce your oath fulfilled."_

There was a sharp crack, and a bond, one that Harry hadn't even known existed, snapped. The ringing died down, and the corridor returned to normal.

Harry was left panting on his knees, wondering what the bloody hell had happened. The river Styx? Wasn't that the river of the underworld in greek mythology?

Hermione gasped, and a look of understanding filled her eyes. "I know what it is! What was different about him all along!"

"He's dead, Hermione!" Harry yelled, tears pooling in his eyes. "He jumped in front of a killing curse meant for me!"

Hermione fell silent.

"But…" Ron managed. "But… Why…?"

Ron looked down at his shoes. "I thought he was a Death Eater."

Hermione couldn't take the silence any longer. "Don't you see? Percy-"

She was interrupted, however, by a tanned hand grabbing her wrist. She screamed.

"Bloody Hell!"

"Merlin's pants!"

Percy Jackson sat up, rubbing his eyes. "What happened?" he asked.

Harry was speechless.

Hermione, however, was not. "You were hit by the killing curse. And you're still alive…"

Percy was suddenly alert. "What?"

"The killing curse," Hermione said. "You were hit."

Harry found his voice. "How are you alive?"

"I," Percy started. He stopped, glancing at their faces. He could tell that they would not believe any more excuses. Only the truth would suffice.

"I, well, um.." Percy rubbed the back of his neck and stared at the floor. "I'm not exactly human, you see. The killing curse only works on mortals…"

He trailed off when he noticed their incredulous faces.

"I'm a demigod."

"You're a _what_?"

 **This was just something I had sitting around. It's the weekend, I thought. Why not post something? So I did. Hope you enjoyed! If not, go eat a pineapple.**


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